The present invention relates to a recording format of a large-capacity recordable type optical disk; and, more specifically, the invention relates to a multilayer large-capacity optical disk that is capable of performing random recording and which has more than one information recording layer.
One example of the track configuration of a conventional optical disk will be described with reference to FIG. 11. A plurality of groove tracks 11 and land tracks 12 are arranged alternately in a radial direction of a disk-shaped recording medium. Each track is wobbled in a radial direction by a relatively small amount. Further, each track is divided into a plurality of arc sectors aligned in a radial direction; and, at a beginning end of each arc sector, a header 6 containing address information is arranged, whereby a recorded region in the arc sector is identified. Therefore, the headers 6 are aligned in a radial direction, that is, they are arranged on plural radials. In this example, the width of each track is approximately 0.6 xcexcm and the groove depth of the groove is approximately 60 nm. In this example, the length of the sector is approximately 6 mm, which corresponds to a user capacity of 2048 bytes. The groove and the land are wobbled in a radial direction by an amplitude of approximately 20 nm. The wobble period is set to 1/232 times the sector length, namely approximately 25 xcexcm. This ratio of 1:232 is chosen so as to fulfil the need for a wobble period to be an integer multiple of the length of the recorded data (channel bit length). The reason for this is to make it possible to generate a recording clock from the wobble easily.
FIG. 11 is a view showing details of the header part at the top end of the track, namely an ID or address data part. In FIG. 11, pieces of the ID or address data are arranged so as to be aligned in a radial direction at a first location 631 and at a second location 632. A track and its neighboring tracks are connected in such a way that the track on the groove 11 connects to such and the track on the land 12 connects to such. In the example of this figure, each ID or address data shown in the figure corresponds to the recorded region that is located on the right side thereof. Further, the ID or address data corresponding to a groove information track 3 on the right side of the figure is arranged at the first location 631; the ID or address data corresponding to a land information track 4 is arranged at the second location 632. That is, the arrangement is such that, for adjacent tracks, locations of the ID or address data are different from each other in a direction along the information track, and for adjacent-but-one tracks, locations of the ID or address data agree with each other in that direction. That is, looking at the configuration on a boundary line between a land track and a groove track, the configuration is such that the location for the ID or address data is divided into first and second regions, and either the first or second ID or address data region is arranged alternately, the same ID or address data region for every other track.
By virtue of this configuration, for example, when the light spot 21 scans the groove 11, either pits of the first or second ID or address data are reproduced and there isn""t a fear that crosstalk from the adjacent tracks would be generated. Therefore, it becomes possible to reproduce the address data allocated in prepits excellently without generating crosstalk. In this example, the address information of the prepits is recorded by means of the 8/16 modulation code (channel bit length: 0.14 xcexcm).
The ID or address data of the header part is formed with small hollows (pits), and these are formed as an unevenness of the substrate or other features together with the groove etc. during the manufacture of the disk.
A phase change type recording layer (GeSbTe) is used as the recording layer, and the recorded mark is formed in the form of a non-crystalline region.
Regarding the foregoing conventional examples, for example, JP-C-2856390 gives a detailed description.
With an arrangement of the ID or address data are provided in the above-mentioned conventional example, the effect of crosstalk arising from the ID or address data of the adjacent tracks can be eliminated. However, there is a problem in that, when the data is reproduced, for example, under a condition such that the ID or address data of a certain track and that of an adjacent-but-one track are both covered with a single light spot, there occurs the effect of crosstalk to a large degree. For example, as shown in FIG. 12, when the light spot is focused on one layer 16 of two recording layers in an optical disk having two layers therein and the reproducing is performed there, a condition may occur as a result of the light spot intercepting the other layer 15. The reason for this is that, since the light spot is not focused on the layer 15, the light spot is out of focus and becomes considerably large; and, therefore, the reading operation is affected by the plural tracks simultaneously. In this case, the ID or address data part aligned in a radial direction will come under a single light spot simultaneously and the effect of the ID or address part data becomes extremely large. Therefore, the extension of the technology to a two-layer recording medium has been substantially impossible.
It is an object of the present invention to provide a recording format for an optical disk that solves the above-mentioned problem and that can easily be applied to a two-layer recording medium.
The following means (or configurations) are used to achieve the object of this invention.
(1) An optical disk having at least one or more information recording layers therein is configured in such a way that there are provided at least a plurality of spiral information tracks each corresponding to one rotation of the disk on the information recording layer, a plurality of information recording units are arranged on the said plurality of tracks, any two of the information recording units that are arranged on all the tracks located in a doughnut region demarcated by two concentric circles with a spacing of 5 xcexcm in a radial direction are arranged such that their top ends are separated by at least 5 xcexcm or more in the circumferential direction. In this configuration, the information tracks, each specified as being wobbled in a radial direction with an almost constant frequency, are used and the amplitude of the wobble is specified to be constant in a radial direction. More preferably, the wobble and the recording unit are arranged in synchronization with each other.
Thanks to this format, even when the recorded region and unrecorded region exist together on the recording layer, any recording units existing in the tracks located in the doughnut region demarcated by the concentric circles with a spacing of 5 xcexcm do not come into alignment to each other in the circumferential direction; and, therefore, when the defocussed light spot moves in the circumferential direction, the light spot will not move from the recorded regions to non-recorded regions or vice versa over a plurality of tracks simultaneously. Therefore, the reproduced signal and the servo signal, which are obtained by the reflected light of the light spot, do not suffer abrupt changes.
In an optical disk having therein a plurality of recording layers that can be accessed from one side of the disk, when one of the layers (a first layer) is being recorded/reproduced, the light spot is defocused (out of focus) on the second layer (with a recording format according to the present invention) to a degree corresponding to the amount of the layer spacing. The size of this defocused light spot is proportional to the layer spacing, and it is common that the size is set to be, for example, 10 times the spot size (0.5-1 xcexcm) that was focused to the diffraction limit of light or more, in consideration of the effect of the inter-layer crosstalk. Therefore, the size of the light spot on the second layer that is not a target layer of recording/reproducing becomes 5 xcexcm or more. Therefore, according to the present invention, the recording unit regions in the tracks located in the doughnut region demarcated by the two concentric circles with a spacing of 5 xcexcm are arranged such that their top ends are shifted by 5 xcexcm or more. This configuration eliminates a fear that the second layer would exert the effect of rapid change on the reflected light and the transmitted light of the light spot.
This mechanism will be described with reference to FIGS. 5A and 5B. FIG. 5A shows the conventional example where the top ends of the recording unit regions (recording units) are aligned in the circumferential direction over a plurality of tracks 11; FIG. 5B shows an example according to the present invention where the top ends of the recording unit regions (recording units) are not aligned in the circumferential direction. Therefore, in the conventional example of FIG. 5A, when the light spot 21 moves from an area where there exist many recording unit regions 13 on which data has been recorded to an area where non-recorded parts are the great majority, there occurs a large change in the reflectance and the transmittance for the whole of the light spot. On the other hand, in the example of FIG. 5B, since there is no occurrence of simultaneous transitions from the recorded regions to unrecorded regions on the tracks under the light spot when the whole of the light spot is considered, the reflectance and the transmittance hardly shows any changes at all. Therefore, a fear that this second layer would exert the effect of rapid change on the reflected light and the transmitted light of the light spot is eliminated, and, consequently, a fear that, due to the inter-layer effect in the multilayer recordable type disk, the quality of the reproduced signal would deteriorate is also eliminated.
The effect of this technique is not limited to a two-layer recording medium. In the single-layer disk as well, the reproducing is conducted with a defocused light spot before the focusing servo unit is in operation. Based on the reflected light of this defocused light spot, an error signal for the auto focusing is obtained, but if there occurs a rapid change, as in the case of FIG. 5A, the focusing servo unit cannot perform well in finding a best focus or it may give a focus offset, hence causing instability in the servo control. According to the present invention, stabilization of a servomechanism is achieved. This stabilizing effect in the servomechanism is effective with respect to a multilayer disk as well.
In this case, by forming the wobble in the information tracks, the timing of reproducing the recorded region can be obtained accurately, and, therefore, when accessing the recorded region, the top end of the recorded region that is shifted in the circumferential direction can be found easily and synchronization therewith can be achieved in a very short time. By setting the wobbles that are adjacent to one another in a radial direction such that their phases are almost equal to one another, even when the recorded region is accessed over the tracks in a radial direction, it is not necessary to achieve synchronization with the wobble or resynchronization can be achieved very quickly. Further, since the frequency of the wobble is almost constant and the geometric loci of the wobbles are in-phase/in-phase in a radial direction, the distance between the information tracks in a radial direction are kept almost constant; therefore, a fear that the wobble would affect the recording/reproducing characteristics is eliminated.
As an additional effect, there is an improvement of the multiple overwriting characteristics. In this regard, it is commonly known that, when overwriting is repeated a number of times in an overwritable type disk, distortion is accumulated at a leader and a trailer of the recorded region. With a format in which the top ends of the recording unit regions are not aligned over a plurality of tracks as specified by the present invention, the effects of the distortion in the leader and the trailer do not center at a single position, but are dispersed and averaged, and therefore, the multiple overwriting characteristics are improved.
(2) An optical disk having at least one or more information recording layers therein is configured in such a way that there are provided at least a plurality of spiral information tracks, each corresponding to one rotation of the disk on the said information recording layer, a plurality of information recording units are arranged on the said plurality of tracks, and an integer multiple of the length of the said information recording unit is different from the length of the track corresponding to one rotation of the optical disk by at least 5 xcexcm or more.
Since the information tracks are configured in a spiral form, a point that moves from the top end of a certain track (referred to as a first track) by the amount corresponding to one rotation of the disk will reach the top end of another track (referred to as a second track). Needless to say, the first and second tracks are close to each other by within 5 xcexcm in a radial direction. Note that the first and second tracks are not necessarily adjacent tracks. For example, in the case where the information tracks are composed of groove tracks and land tracks (land-and-groove structure) as indicated in the later-described section (7) and thereafter, a continues spiral structure that is made up of contiguous tracks is not necessarily a single spiral. More particularly, if the groove tracks are configured such that one groove track is connected to the next groove track after one rotation of the disk and the land tracks are configured such that one land track is connected to the next land track after one rotation of the disk, the disk has a structure of two spirals that consists of one spiral made up of a series of tracks on the land and another spiral made up of a series of tracks on the groove. This particular structure is generally called a double spiral. In this case, if the above-mentioned first track is on the groove, the second track is also on the groove, but there is a land track between these two groove tracks, and, therefore, the first and second tracks are not the adjacent tracks. The recording unit regions are arranged without spacing from the first track to the second track and so on. Since an integer multiple of this recording unit region does not agree with the length of the track, the locations of the top ends of the information recording units on the first track and on the second track are shifted in the circumferential direction. Because of this mechanism, virtually the same arrangement of the recording unit regions as that of the above-mentioned section (1) is realized and the same effect is achieved.
(3) An optical disk is configured in such a way that, among a combination of two integers N and M, such that the integer N times the length of the above-mentioned information recording unit agrees with the integer M times the length of the above-mentioned track, a minimum combination of N and M (referred to as xe2x80x9cn and mxe2x80x9d) is found and the integer m is more than 5.
By this configuration, the top ends of the information recording units on the tracks that are formed continuously in the form of a spiral, similarly to that of the above-mentioned section (2) do not coincide with one another in the circumferential direction for m tracks. Here, assuming that the tracks are of the land and groove structure and the width of the track is approximately 0.5 xcexcm, a fact that m is 5 or more indicates that the disk can be configured such that the top ends of the recording units do not agree with one another in the circumferential direction over a radial range of 0.5xc3x972xc3x975=5 xcexcm or more. (In this case, it is necessary to configure the recording unit regions on the land track and the recording units on the groove track so that they are shifted from each other.) Therefore, as a result, the configuration is the same as that of section (1) and the effect is also the same.
(4) An optical disk that has at least one or more information recording layers and has a plurality of spiral tracks, each consisting of a groove and/or a land, and each corresponding to one rotation of the disk on the said information recording layer, is configured in such a way that the said track is formed so as to be wobbled in a radial direction, there exists an integer j such that the integer j times the length of the said wobble agrees with the length of one track, the length of the information recording unit arranged on the track is equal to k times the period of the said wobble, and representing a least a common multiple of the integers j and k as L, the integer L is set to 5 times the integer j or more.
This agrees with the feature of above-mentioned section (3) and, consequentially, with respect to a relation between the information recording unit and the track. That is, since the least common multiple of the integers j and k is L, L=kxc3x97n and L=jxc3x97m and the integers n and m are coprime to each other. In other words, the integers n and m are a minimum combination of a combination of N and M such that integer N times the length k of the information recording unit agrees with integer M times the length j of the track.
Since in this means the information tracks are constructed so as to be wobbled and the length of the information recording unit and the length of the track are each specified so as to be an integer multiple of the wobble in addition to the feature of above-mentioned section (3), it becomes easy to achieve synchronization with the information recording unit, the track, and finally the recording information itself using the periodic signal obtained from the wobble. Moreover, since one rotation of the track is composed of integer pieces of wobbles, the wobbles are in phase between the adjacent tracks; and, therefore, a stable wobble signal can be obtained, and there is no adverse effect against the reproduced signal.
(5) An optical disk having at least one or more information recording layers therein is configured in such a way that there are provided at least a plurality of spiral information tracks, each corresponding to one rotation of the disk on the said information recording layer. There are provided plural pieces of address data on the said track, any two of pieces of the ID or address data that are arranged on all the tracks located in a doughnut region demarcated by two concentric circles with a spacing of 5 xcexcm in a radial direction are arranged such that their top ends are separated by 5 xcexcm or more in the circumferential direction.
By virtue of this configuration, since pieces of the recording address data are not aligned mutually in the circumferential direction for tracks existing in the range of a radial increment of 5 xcexcm, the effects of defocused pieces of address data for a plurality of the tracks are not received simultaneously; and, consequently, the reproduced signal and the servo signal both obtained from the reflected light of the light spot, do not suffer abrupt changes.
In the optical disk having a plurality of recording layers that can be accessed from one side of the disk, when one of the layers (a first layer) is being recorded/reproduced, the light spot is defocused (out of focus) on the second layer (with a format according to the present invention), to a degree corresponding to the spacing between the layers. The size of this defocused light spot is proportional to the spacing between the layers, and it is common that the size of the defocused light spot is set to be 10 times the spot size (0.5-1 xcexcm) or more that is focused to the diffraction limit of light. Therefore, the size of the light spot on the second layer that is not a target layer of recording/reproducing becomes 5 xcexcm or more. Therefore, by shifting the top ends of pieces of the address data on the track by 5 xcexcm or more for tracks located in the range of a radial increment of 5 xcexcm as specified by the present invention, a fear that this second layer would exert the effect of rapid change on the reflected light and the transmitted light is eliminated.
The effect of this feature is not limited to a two-layer recording medium. In the single-layer disk as well, the reproducing is performed with a defocused light spot before the focusing servo unit is in operation. Based on the reflected light of this defocused light spot, an error signal for the auto focusing is obtained, but if there occurs a rapid change as in the case of FIG. 5A, the focusing servo unit cannot perform well in finding a best focus or it may give a focus offset, hence causing instability in the servo operation. According to the present invention, stabilization of a servomechanism is achieved. This stabilizing effect in the servomechanism is effective with respect to a multilayer disk as well.
As an additional effect, the disk forming characteristics are improved. It is known that the disk substrate is normally formed by molding a thermoplastic resin, such as polycarbonate, in a mold, and that, if the embossed marks of the address data center in a part of the disk in the circumferential direction, the embossed marks cause adverse effect on a flow of the resin during molding. Therefore, there may exist a phenomena in which a molded track deforms or birefringency increases locally. If pieces of the address data are arranged so as not to be aligned for a plurality of tracks, as called for by the present invention, the effects of their distortions do not center at a single position, but are dispersed and averaged; consequently, the molding characteristics are improved and the tolerances of molding conditions are widened, and, accordingly, the manufacture of the disk becomes easy.
(6) An optical disk that has at least one or more information recording layers and has a plurality of spiral tracks, each consisting of a groove and/or a land and each corresponding to one rotation of the disk on the said information recording layer, is configured in such a way that the said tracks are wobbled in a radial direction. The address data arranged on the track is arranged so as to be separated from the address data of the adjacent track in the circumferential direction by the amount of an integer multiple of the wobble period.
Because of this configuration, pieces of the address data do not center at the same position in reference to the circumferential direction as is the case of the feature of the above-mentioned section (5), and therefore the same effect as the above-mentioned section (5) can be achieved.
Further, since the amount of the separation is an integer multiple of the wobble period, the top end of the recorded region that is shifted in the circumferential direction can be found easily, and synchronization can be achieved in a very short time. By setting the phases of the wobbles that are adjacent to each other in a radial direction, even when the recorded region is accessed over the tracks in a radial direction, it is not necessary to achieve synchronization with the wobble again, or resynchronization can be achieved very quickly. Further, since the frequency of the wobble is almost constant and the wobbles are in-phase in-phase in a radial direction or radially ajacent wobbles are in-phase, the distance between the information tracks in a radial direction is kept almost constant; and, consequently, a fear that the wobble would affect the recording/reproducing characteristics is eliminated.
Note that the phase of the wobble and the (top end) location of the recording unit region are in synchronization with each other, which is evident from the fact that the phase of the wobbles having approximately constant frequency are in-phase in-phase in a radial direction and the fact that the amount of the separation between the recording unit regions in the circumferential direction is an integer multiple of the wobble period.
Moreover, since the reproducing of the address data and the timing generation of the recording/reproducing can be performed using the wobble, reliable recording/reproducing can be performed stably. If the number of wobbles for one rotation of the track is chosen to be an integer number xc3xcian integer multiple of the wobble period being the length of one round of the trackuj, the phases of the wobbles are in-phase between the adjacent tracks, which is more preferable.
(7) Further, an optical disk is configured in such a way that the above-mentioned address data is formed in the form of embossed pits, and the embossed pits are arranged on an extension line of the boundary line between the groove track and the land track. A groove interrupted part is arranged on the embossed pit parts that are on four most adjacent tracks, including two tracks on whose boundary the embossed pits are arranged, in order that the groove does not exist there.
Because of this, the reproduction signal of the embossed pits of the ID or address data part can be reproduced free from the effect of the adjacent tracks, in addition to the effects of the above-mentioned sections (5) and (6); therefore, the quality of the reproduced signal of the embossed pits signal is improved, and this scheme is suitable for high-density recording. Moreover, since the embossed part and the groove can be made to not exist simultaneously, mastering can be carried out using a single beam in manufacturing a master (original record) for manufacturing a substrate; and, therefore, adjustment of the mastering apparatus is made easy. An example of application of this feature is shown in FIG. 1 and FIGS. 2A, 2B.
(8) An optical disk is, in addition to the feature of section (6), specified such that a region exists in which the groove is interrupted, the ID or address data is formed in the form of the embossed pits, and the embossed pits are arranged on the center line of the groove track at the interrupted part of the groove.
By this configuration, the quality of the reproduced signal of the embossed pits is improved in addition to the effects of the above-mentioned sections (5) and (6), and this configuration is suitable for high-density recording. Moreover, since the embossed part is on the extension line of the groove, the embossed pits can be formed as the presence and the absence of a groove; hence, a single beam is used to do the mastering in manufacturing the master (original disk) for manufacturing a substrate, and, consequently, adjustment of a mastering apparatus becomes easy and the disk manufacturing cost can be reduced. An example of application of this feature is shown in FIG. 13C.
(9) An optical disk is configured in such a way that the embossed pits are arranged also on the centerline of the land track; and, at a part of the groove track adjacent to a part of the land track where the embossed pits are arranged, the groove is interrupted.
By this configuration, the present invention can be applied to a land-and-groove type track, and, therefore, the configuration is suitable for high-density recording. An example of application of this feature is shown in FIGS. 13A and 13B.
(10) An optical disk is configured in such a way that the information recording units are arranged so as to be separated between the adjacent tracks in the circumferential direction, and the embossed pits representing all of or part of the address data are arranged so as to be aligned in a radial direction (at the same location with respect to the circumferential direction).
By this configuration, pieces of the ID or address data are arranged at the same location in the circumferential direction, and, therefore, rapid access to the recorded region is made easy. The information recording units are arranged so as to be separated from one another in the circumferential direction; and, therefore, the same effect as described in the above-mentioned section (1) can be obtained. When applying this feature, it is preferable that the length of the address data in the circumferential direction is not more than 3 xcexcm or so and that the spacing of the address data is smaller than the length of the information recording unit.
More preferably the address data is divided into pieces of partial information whose length is not more than 3 xcexcm or so, which are arranged so as to be dispersed in the circumferential direction with a spacing not less than 50 xcexcm and not more than 1 mm. In this case, for example, one piece of partial information is chosen to represent information of one bit, and about 50 pieces of partial information are arranged so that one address data is composed thereof. By involving redundant information in the above-mentioned 50 pieces of partial information, the address data can be reproduced reliably and surely even when some of the pieces of the address data can not be reproduced due to defects etc. It is recommendable that the top end location of the information recording unit is arranged so as to be separated from that of the adjacent track in the circumferential direction by the amount of, for example, an integer multiple of the arrangement spacing of the above-mentioned partial ID or address data. Moreover, it is preferable that the track is wobbled as in the above-mentioned example to obtain timing of reproducing the ID or address data more surely. In that case, more preferably, the number of wobbles for one rotation of the track is chosen to be an integer multiple (an integer multiple of the wobble period being the length of one rotation of the track), because the the wobbles are in-phase/in-phase/in-phase between the adjacent tracks. An example of application of this feature is shown in FIG. 7 through FIG. 9.
(11) Moreover, an optical disk is configured in such a way that the optical disk has at least two or more information recording layers that can be accessed from one side of the disk, to which the features of the above-mentioned sections (1) through (10) are applied, and at least one recording layer is chosen to be a recordable type layer or an overwrite type layer.
By this configuration, a single sheet of the disk can store mass information as much as two times the information of the single-layer disk or more, and the signal crosstalk and disturbance between the signals from the information recording layers can be prevented by virtue of the effects described in sections (1) through (10). Therefore, a large-capacity optical disk that is surely a recordable type and has a multiple recording layers therein can be provided.
Other and further objects, features and advantages of the invention will appear more fully from the following description.